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A Handbook of Biology

RH GRØÜPÏÑG

Rh antigen found on

RBC is similar to one

present in Rhesus

monkey (hence Rh)

Rhesus (RH) factor

is another antigen

found on RBC.

Rh+ve means the

presence of Rh

factor and Rh-ve

means absence of

Rh factor. Nearly 80%

of humans are

Rh+ve.

1

2

3

BLØØD ÇØÅGÜLÅTÏØÑ



It is a mechanism for haemostasis (prevention of blood loss through

injuries). At the site of injury, following events occur:

Clumped

platelets

and

tissues

release

thromboplastin.

It

forms

thrombokinase

(prothrombinase)

enzyme.

Thrombokinase

hydrolyses prothrombin to thrombin enzyme in

presence of Ca²⁺. Thrombin converts soluble

fibrinogen to insoluble fibrin. Fibrin threads trap

dead and damaged blood cells to form clot

(coagulum). Calcium plays a very important role in

blood clotting.

ËRÝTHRØBLÅSTØSÏS FØËTÅLÏS



It is Rh incompatibility between the Rh-ve blood of a pregnant mother

and Rh+ve blood of the foetus.



Rh antigens do not get mixed with maternal blood in first pregnancy

because placenta separates the two bloods.



But during first delivery, the maternal blood may be exposed to small

amount of foetal blood (Rh+ve). This induces the formation of Rh

antibodies in maternal blood.



In case of subsequent pregnancies, the Rh antibodies from the mother

leak into the foetal blood (Rh+ve) and destroy the foetal RBCs. This is

fatal to the foetus or cause severe anaemia and jaundice to the baby.

This condition is called erythroblastosis foetalis.



It can be avoided by administering anti-Rh antibodies to the mother

immediately after the first delivery.